This invention relates to a rotameter-type flowmeter, and more particularly to such a flowmeter having means for adjusting the linearity (i.e., means for normalizing) of the output readings of the flowmeter.
Generally, a rotameter-type flowmeter includes a vertically disposed rotameter tube of circular cross section through which flows the fluid whose flow rate is to be measured. This rotameter tube is tapered typically with its smallest diameter at its bottom. A float is disposed within the rotameter tube and is movable axially therewithin in response to changes in flow rate through the rotameter tube --the higher the flow rate, the higher the flow rises within the rotameter tube. Of course, as the float rises higher in the tapered rotameter tube, the flow area between the walls of the rotameter tube and the float gets progressively larger. A magnet is operably movable with the float. This float magnet may be incorporated in the float or it may be remotely located from the float, but operatively coupled thereto by means of an extension rod or the like. A magnetic follower is mounted adjacent the float magnet and it is magnetically coupled to the float magnet so that it moves in response to movement of the float (i.e., in response to changes in the flow rate of the fluid).
As shown in the co-assigned U.S. Pat. No. 3,535,932, and in U.S. Pat. No. 3,065,635, the follower magnet is an elongate helical magnet disposed generally parallel to the path along which the float magnet moves (i.e., beside the rotameter tube). This helical follower magnet is journalled in suitable bearings so as to rotate freely about its longitudinal axis. A pointer is carried by the follower magnet. In operation, the leading edge of the helical follower magnet is continuously attracted to the float magnet. Thus, as the float magnet moves longitudinally within the rotameter tube, the helical follower magnet rotates about its longitudinal axis and the pointer is calibrated to indicate the flow rate of the fluid flowing through the flowmeter.
In another type of rotameter-type flowmeter, such as is shown in U.S. Pat. No. 3,315,523, a follower magnet in the shape of a disk is mounted on a shaft with the latter being rotatable about its longitudinal axis. Generally, the axis of the shaft on which the follower magnet is mounted is perpendicular to the path along which the float magnet is movable. The disk follower magnet is magnetically coupled to the float magnet and it is rotatable with its shaft in response to movement of the float magnet along its path. The shaft carrying the follower magnet also carries a pointer movable relative to a scale so as to indicate flow rate.
Generally, rotameter-type flowmeters, such as those described above, have worked well. These flowmeters are in general unaffected by vibration, extreme ambient temperature conditions, and they operate reliably in dirty or corrosive environments. However, a long standing problem has been associated with these flowmeters, viz, a non-linear relationship between the actual flow rate and the movement of the pointer. More particularly, the output of prior art rotameter-type flowmeters was found to be non-linear due to the geometry (i.e., the shape) of the metering float and the hydraulic characteristics of the fluid being metered. This nonlinearity would show itself as a bow-shaped curve, generally as is shown by the solid line curve in FIG. 6, when the float travel position is plotted as a percentage of full scale flow rate. For example, the linear deviation of a conventional rotameter-type flowmeter might be 7% of its full scale reading at a float position of 50% of its full scale travel and may have no deviation at its 0% and 100% float travel positions.
Heretofore, at least two different schemes were proposed to linearize or normalize this non-linearity problem. As shown in the above-noted U.S. Pat. No. 3,535,932, a non-magnetic (e.g., aluminum) plate was disposed adjacent the helical follower magnet. Then, a number of magnetic flux diverting plates were secured in place on the non-magnetic plate adjacent the helical follower magnet at locations corresponding to points of deviation between the actual and linear (or normal) output curves of the flowmeter. By positioning the flux diverting plates on either side of the follower magnet, depending on whether while the deviation from the linear curve is positive or negative, it was possible to correct each deviation more or less independently so that the actual and linear outputs of the flowmeter were essentially the same.
However, this prior art system required that the actual output characteristics of each flowmeter be established independently and that the number of and the location of the flux diverting plates be individually determined while calibrating each flowmeter. Also, this linearizing technique required that each flux diverting plate be secured in position on the non-magnetic plate in its respective position as determined during calibration. This, of course, required considerable time of skilled instrument calibration technicians and resulted in considerable additional labor costs.
In U.S. Pat. No. 3,977,248, another technique for linearizing a rotameter-type flowmeter is disclosed. In this patent, a rotary disk follower magnet is disclosed which has a weight eccentrically mounted on the follower magnet shaft. This weight is positioned angularly relative to an indicator needle (e.g., a pointer) also carried by the shaft so that the moment of the eccentric weight compensates for the hydraulic characteristics of the flowmeter and thus linearizes the flowmeter output. As disclosed in this prior patent, the eccentric mass is carried on a threaded stud affixed to and rotatable with the follower magnet shaft. To calibrate the flowmeter, it is necessary to select a mass of appropriate weight and to thread the mass radially inwardly or outwardly on the threaded shaft stud so as to apply the desired moment on the shaft.
Among the many objects and features of the present invention may be noted the provision of an improved rotameter-type flowmeter, generally as described above, in which the output indications of the flowmeter may be readily calibrated (or adjusted) to be substantially linear;
The provision of such a flowmeter in which the magnet coupling between the float magnet of the follower magnet may be readily varied so as to adjust the position of the pointer relative to the float position in such manner as to be the equivalent of the degree of non-linearity of the hydraulic characteristics of the flowmeter;
The provision of such a flowmeter in which the zero positions, scale span, and linearity of the output of the flowmeter can be readily set to correspond to the hydraulic characteristics of a flowmeter or fluid;
The provision of such a flowmeter which utilizes a single scale and transmitting cam for a wide range of non-linear flow characteristics within a given range of fluid viscosity;
The provision of such a flowmeter in which the magnetic coupling between the float and the follower magnets is of sufficient strength so as to provide adequate force or stiffness as to effectively operate various flowmeter transmitters and so as to hold an indicator at any desired position;
The provision of such a flowmeter which utilizes common scales and transmitting cams and which is capable of measuring flow rates of various fluids; and
The provision of such a flowmeter which is more reliable and accurate than other prior art flowmeters, particularly prior non-linearized flowmeters, and which may be more readily and expensively calibrated in prior normalized (or linearized) rotameter-type flowmeters.
Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.